Environmental control system and method for storage buildings

ABSTRACT

A method and system for controlling the environment of storage facilities, including produce and livestock storage facilities, and the like, is described. Movement of air within the facility is accomplished by air-handling units or fans. The speed of each fan is controlled by a variable-speed drive, allowing the fans to run at speeds below full capacity. Environmental parameters, such as temperature or humidity, are monitored to determine the existing state of the environment which is then compared to a desired state. The speed of the fans or air-handling units is adjusted to alter the existing environmental state, bringing it in alignment with the desired state. The fans or air-handling units are operated continuously, typically at reduced capacity. Other various facets are included with the system and method, including the control of the admittance of external air into the storage facility.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.09/621,509, filed Jul. 21, 2000, now U.S. Pat. No. 6,467,695 B1, whichissued Oct. 22, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to environmental control ofstorage buildings and facilities. More particularly, the presentinvention relates to the control of such parameters as temperature,humidity, and carbon dioxide (CO₂) within a storage facility whereinproduce or like commodities are stored.

2. State of the Art

Produce providers often desire to store fruits and vegetables forextended periods of time. Produce is often stored to maintain adequatesupplies during periods when a particular commodity is out of season.Processors of fruit and vegetables increasingly desire commercialgrowers to store their products for longer and longer periods of time.Indeed, processors require a year-round supply of produce whilerequiring that the quality of such produce remain high.

To store produce for extended periods of time without substantialdegradation of quality, it becomes imperative to control the environmentin which the produce is stored. Control of the storage facilityenvironment may include the control of, for example, temperature,humidity, and air quality including carbon dioxide (CO₂) content.Typically, control of such parameters in a storage facility environmententails movement of air within the facility. Oftentimes, this includesintroduction of air from outside the facility. Other times it may simplyinvolve the circulation of existing air inside the storage facility.

One method of controlling the environment has been to place fans orair-handling units in the facility. The fans may be turned on when thetemperature rises above a predetermined upper level and shut off whenthe temperature of the facility reaches a predetermined lower level. Asystem of this type is described in U.S. Pat. No. 3,801,888 to Faulkner.This type of system utilizes the fans at full power, allowing them tocool the facility at a relatively quick pace, but also allowingtemperatures or other environmental parameters to change rapidly withina specified range. Rapid changes in temperature or temperature spikesmay often cause a temperature-induced shock to the stored inventory,ultimately resulting in quality degradation. Similarly, rapid changes inother environmental parameters may degrade the quality of the storedcommodity.

Some systems have sought to utilize multi-speed fans such as isdescribed in U.S. Pat. No. 3,896,359 to Olander et al. Such a system isimplemented with the desire of allowing temperature or otherenvironmental changes to take place at a slower rate. However, eventhese systems do not allow the desired flexibility in controlling achosen environmental parameter within the storage facility. Such systemsemploy low- and high-speed control of the fan or air-handling unit.While this allows for a stepped transition from one temperature toanother, it simply reduces the magnitude of any temperature spike ratherthan providing a continuous control of temperature within the storagefacility. This is because the high- and low-speed settings eachcorrespond to a defined range of operability. Thus, for example, incontrolling temperature, the fans will remain inoperative if thetemperature of the facility is within a defined temperature range. Thefans will then operate at a low-speed setting once the temperatureincreases into a second defined range. Finally, the fans will operate ata high-speed setting if the temperature increases into a third definedrange. The process will reverse itself as the temperature decreases.However, the ranges cannot be defined too tightly, otherwise the fanwill be constantly starting and stopping as the temperature fluctuatesbetween the first and second range. On the other hand, the definedranges may not be set too broadly. If the ranges are too broad, then thetemperature will increase to the point where the fans will be operatingat the high-speed setting for extended periods of time in an attempt tobring the temperature back to an acceptable value. Also, depending onthe commodity being stored, broad parameter ranges may simply not beacceptable from a quality standpoint.

Another important consideration in the environmental control of astorage facility is the efficient use of power. With most systemsrelying on fans that are cycled between on and off positions, or thosesystems having high/low-speed settings, power consumption is ofparamount concern to the facility operator. Storing commodities forextended periods of time requires a significant consumption of powerwith existing systems and methods. The cost of such power, whileinitially resting with the facility operator, ultimately gets passedalong to the consumer in the form of higher prices at the market. Thus,an efficient and accurate environmental control system for storagefacilities would be of benefit to more than just the facility operator.

In view of the shortcomings in the art, it would be advantageous toprovide an environmental control system for a storage facility whicheffectively controls specified environmental parameters while consuminga reduced amount of energy. Such a system or method should be simple toemploy in existing as well as new storage facilities.

BRIEF SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a method is provided forcontrolling the internal environment of a storage facility, such as astorage bin for produce. The method includes the steps of providing afan, or a plurality of fans, for moving the internal air of the storagefacility. The fans are continuously operated within the storagefacility. The fans may be operated continuously at a speed which isbelow their full capacity for continuous parameter control and reducedpower consumption. The system monitors a parameter indicative of theinternal environment of the storage facility. For example, a temperaturesensor may be employed to monitor the internal temperature of thestorage facility. Once the temperature has been monitored, the speed ofthe fans may be altered accordingly. For example, if the internaltemperature needs to be reduced, then the fans may be operated at ahigher rotational speed, increasing the air movement within the storagefacility. Likewise, if the air temperature needs to be increased, thefan speeds will again be altered to accomplish this requirement. Thesame method may be applied in monitoring other parameters and changingthe rate of air flow to obtain a desired value for the given parameter.

Additionally, environmental parameters outside of the storage facilitymay be monitored to assist in the regulation of airflow inside thestorage facility. For example, outside air temperature may be monitoredand compared to the desired facility temperature to determine whetheroutside air should be admitted into the facility via a ventilationinlet. Various restrictions may be placed on the admittance of outsideair, such as prohibiting outside air into the facility if the outsidetemperature is above a specified maximum or below a specified minimum.

In accordance with another aspect of the present invention, a system isprovided for controlling the internal environment of a storage facility.The system includes a fan or multiple fans which may be adapted tooperate continuously. The fans may be operated continuously at a speedwhich is below their operational capacity. The fans are placed to movethe internal air of the storage facility during operation. Each fan iscoupled to a variable speed drive for controlling the operational speedof the fans. At least one sensor is employed to monitor one or moreinternal environmental parameters of the storage facility such astemperature, humidity, gas levels, or chemical levels. The sensor iscoupled to an electronic control unit which is also coupled to thevariable speed drive. The sensor provides a signal to the electroniccontrol unit, the signal representing a measured value of an internalenvironmental parameter. The electronic control unit then provides asignal to the variable speed drive based upon the sensed parametercausing the associated fan to vary in speed accordingly.

Additional elements may be configured with the system to render greatercontrol and flexibility. For example, sensors monitoring an externalenvironment may be coupled to the electronic control unit to assist indetermining fan speed. Ventilation inlets or outlets may also be coupledto the electronic control unit for controlling flow of air into and outof the facility, respectively.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing and other advantages of the invention will become apparentupon reading the following detailed description and upon reference tothe drawings in which:

FIG. 1 is a plan view of a storage facility in accordance with certainaspects of the present invention;

FIG. 2 is an elevational view of the storage facility of FIG. 1 takenalong the section line 2—2;

FIG. 3 is a plan view of a storage facility according to another aspectof the present invention;

FIG. 4 is a schematic representation of an environmental control systemin accordance with certain aspects of the present invention;

FIG. 5 is a block diagram illustrative of the logic employed in oneembodiment of the invention; and

FIG. 6 is a block diagram illustrative of the logic implementedaccording to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a storage facility 10 implementing an environmentalcontrol system according to a particular embodiment of the invention isdepicted in plan view. The storage facility includes exterior walls 12which separate the storage facility from an external environment. A fan14, which may be a simple industrial sized fan or any other type ofair-handling unit suitable for use in such a facility, is housed at oneend of a main air duct 16 or plenum. An interior wall 18 serves as abarrier between the main air duct 16 and a storage area 20, alsoreferred to herein as the storage bin 20. A series of secondary orlateral air ducts 22 pass through the interior wall 18 from the main airduct 16 to the storage bin 20. Each lateral air duct 22 includes aplurality of vents or openings 24 which allow for distribution of airthroughout the storage bin 20.

A ventilation inlet 26 is located in an exterior wall 12 near the fan14. The ventilation inlet 26 allows for external air to be introducedinto the main air duct 16 when desirable. An outside sensor 28 islocated external to the facility 10 to monitor a defined environmentalparameter. For example, the temperature or humidity of the external airmay be monitored to determine the suitability of external air and thedesirability of admitting such air. It is contemplated that one or moresensor(s) may be used in such a facility to monitor various externalenvironmental parameters.

Generally, airflow is induced by the fan 14 and travels down the mainair duct 16 as indicated by directional arrows 30. Airflow thencontinues into the lateral air ducts 22 as indicated by directionalarrows 32 and into the storage bin 20 through the ventilation openings24 of the lateral air ducts 22. The air may then be exhausted throughventilation outlets or returned to the main air duct 16 as more fullydescribed below. The airflow provided by the fan 14 is used to controlthe internal environment of the storage bin 20. The circulation of air,including the recirculation of internal air or the introduction ofexternal air and exhausting of internal air, when necessary, can becontrolled to manipulate various internal environmental parameters. Suchparameters may include, for example, temperature, humidity or CO₂content of the facility.

Referring now to FIG. 2, an elevational view of the facility 10 isdepicted as indicated by sectional line 2—2 of FIG. 1. The ventilationinlet 26 is shown to be adjusted by an actuator 34. The ventilationinlet 26 is shown to be a hinged door or hatch actuated by a hydraulicor pneumatic cylinder. The configuration as shown, with the inlet 26swinging inwardly, allows the inlet 26, when closed, to permit only therecirculation of air from within the facility, as depicted bydirectional arrow 40. When the inlet is open only external air isintroduced into the main air duct 16 as indicated by directional arrow42. When the inlet 26 is positioned at an intermediate position, amixture of recirculated air and external air is introduced into the mainair duct 16. While the above-described embodiment is simple andeffective for the purpose of introducing external air into the storagefacility, it is to be understood that any method of creating andactuating a ventilation inlet known in the art is considered to bewithin the scope of the disclosed invention.

A ventilation opening 36 is formed within the interior wall 18. Throughthe ventilation opening 36, the upper limit of a produce pile 38 may beseen. While not shown in FIG. 1, the produce pile is located in thestorage bin 20 over the lateral air ducts 22. In addition to allowingone to view the inside of the storage bin 20, the ventilation opening 36also allows air to return from the storage bin 20 and back into the mainair duct 16. Thus, when the ventilation inlet 26 is closed, air iscirculated through the main air duct 16 as indicated at 30, through thelateral air ducts 22 as indicated at 32, up through the produce pile 38,and through the ventilation opening 36 back to the main air duct 16 asindicated by directional arrows 40. Alternatively, adjustablevents/louvers may be placed over the ventilation opening 36 to helpcontrol recirculation.

When the ventilation inlet 26 is fully opened, external air only isallowed into the main air duct 16 as indicated by directional arrow 42.When the door is in the midway position, the external air combines withthe recirculated air to create a mixed flow. During external air ormixed flow operation, it may be necessary to exhaust some of the air dueto a positive pressure experienced in the storage bin 20. While notshown in either FIG. 1 or 2, an exhaust vent may be placed in anexterior wall 12 or in the ceiling of the storage bin 20 to accommodatesuch exhaust. While various types of vents may be utilized, an exhaustvent with gravity louvers is often sufficient. This type of vent allowsair to exhaust to an external environment when a positive pressure ispresent on the interior of the building, while prohibiting air flow whenthe interior of the building experiences a negative or equilibratedpressure. The louvers thus open when an internal positive pressure isexperienced and close, due to gravity, in the absence of a positivepressure.

Additional sensors 44 and 46 are shown in FIG. 2. A supply air sensor 44is located in the main air duct 16 and allows for the monitoring of achosen parameter of the supply air prior to its introduction into thestorage bin 20. A return air sensor 46 is located near the ventilationopening 36 to similarly monitor the air as it returns from the storagebin 20. Thus, the air is monitored at various locations to assist indetermining whether any adjustments need to be made. Adjustments wouldtypically include changing the rate at which air is circulated and/oradjusting the amount of external air being introduced into the facility10. These adjustments, and the logic of making such adjustments, will bediscussed in greater detail below.

A chosen parameter may be monitored in the main air duct 16 to preventthe introduction of air having a far greater or lesser temperature (orother chosen environmental parameter) than that of the storage bin, 20.A sudden change in the temperature or other property of the air (e.g.,humidity or CO₂ concentration) surrounding the produce may cause thequality of the produce to unacceptably deteriorate. Thus, in conjunctionwith monitoring the chosen parameter, the speed of fan 14 can be varieduntil the properties of the air in the main air duct 16 more closelymatch, or are within a specified range relative to, the properties ofthe air in storage bin 20. The ratio of external air to recirculated airmay be altered using the ventilation inlet 26 to modify the environmentin chamber 16. Additionally, in some applications, heating or coolingcoils, or some other conditions apparatus, may be used to further adjusta selected parameter of the air in the main air duct 16 prior to itsintroduction into the storage bin 20.

Turning now to FIG. 3, a sectional plan view of the storage bin 20 isshown wherein additional components are shown and described. The producepile 38, as described previously, sits atop the lateral air ducts 22.Air flow is directed through the ventilation openings 24 (as shown inFIG. 1) and through the produce pile as generally indicated bydirectional arrows 48. As described above, circulation of the airtypically causes the air to return to the main air duct 16 forrecirculation. However, in certain circumstances, it may be desirable tocreate an exchange of air by exhausting air at a more rapid pace. Such atechnique would be desirable, for example, to remove air having a highercontent of CO₂ than is desired.

An auxiliary fan 50 is placed at the upper end of the storage bin 20near an exhaust vent 52 such as a louvered gravity vent. An auxiliaryventilation inlet 54 is located in an exterior wall 12 opposite the fan50 and exhaust vent 52. The ventilation inlet 54 may be operated by anactuator 56, as shown, or by other suitable means, such as, for example,gravity louvers. When in operation, the auxiliary fan 50 draws externalair through the ventilation inlet 54, across the storage bin 20, and outthrough the exhaust vent 52 as indicated by directional arrows 58. Asensor 60 is located in the storage bin to monitor a desired parameter,such as the CO₂. It is understood that the actual physical location ofthe fan 50 and associated vents 52 and 54, while typically locatedtoward the vertical extremes of the facility, will depend on the actuallayout of the storage facility in which they are employed and may bearranged in various configurations to accomplish the same or similarresults.

An auxiliary system, such as that depicted in FIG. 3, assists inmaintaining various internal environmental parameters when control ofthe main system is limited by the external environmental parameters, forexample, during an extended period of time the external temperature (asmeasured by sensor 62) may be either too warm or too cold to open themain inlet door 26 for the introduction of fresh air. In such a case, itis still desirable to control the oxygen, carbon dioxide or other gaslevels within the storage bin 20. The auxiliary system shown in FIG. 3may be utilized to introduce just enough external air to control the gaslevel without unduly influencing other internal environmental parameterssuch as temperature or humidity. The auxiliary fan 50 and ventilationinlet 54 may be controlled simultaneously to introduce the proper amountof external air in such a situation.

Alternatively, fan 50 may be used as the primary control of theenvironment within the storage facility. Fan 14 may operate at aconstant speed to maintain air circulation within the storage facility.Additionally, inlet 26 (FIGS. 1 and 2) need not be present, makingventilation inlet 54 (FIG. 3) the primary or sole source of externalair. The speed of the fan 50 and/or the amount of external air beingintroduced into the storage bin 20 through ventilation inlet 54 may beadjusted to control the environment. In such a configuration, fan 14(FIGS. 1 and 2) may be used to simply circulate the air from the storagebin 20 throughout the produce pile 38. Such a system enables control ofparameters such as temperature, humidity, and carbon dioxideconcentration. Determination of the needed adjustments may includeconsideration of external environmental parameters measured by sensor 62and/or environmental parameters within the storage bin measured, forexample, by sensor 60.

Referring now to FIG. 4, a schematic of the environmental control system100 of the present technique is depicted. A first fan 102 is shown whichmay be taken to represent the main fan 14 located in the main air duct16. A second fan 104 is also shown, and may be taken to represent theauxiliary fan 50 shown in FIG. 3. Each fan 102 and 104 is connected to avariable-speed drive 106 and 108, respectively. There are numerous typesof variable-speed drives commercially available, each having variousbenefits and features. It is contemplated that the present system andmethod may be practiced utilizing different types of variable-speeddrives for varying the rotational speed of the fans 102 and 104. Forexample, a variable-speed drive of the type employing a magnetic clutchwould be suitable for use in the present technique. Such a drive variesthe current supplied to the clutch causing the magnetic force to varybetween the clutch and the shaft. This allows a certain amount of slipto occur between the shaft and the clutch. Ultimately, the rotationalspeed is varied by varying the amount of slip allowed in the magneticclutch. While such a drive, and numerous others, may be suitable for usein practicing the present technique, the drives utilized in thepresently disclosed embodiment are variable-frequency drives, sometimesreferred to as inverter drives.

As known by those skilled in the art, a variable-frequency drive (VFD)is an electronic controller that adjusts the speed of an electric motorby modulating the power being delivered. More specifically, the speed ofthe electric motor is controlled by modulating the frequency of thepower being supplied. The standard frequency of AC power in the UnitedStates is 60 Hz. A standard electric motor constructed for use in theUnited States is designed to be operated with a 60 Hz power supply. Adecrease in the frequency of the power supply will result in acorresponding decrease in motor speed. For example, an electric motorthat rotates at 100 rpm with a 60 Hz power supply would run at 50 rpmwhen the power supply is reduced to 30 Hz.

Referring still to FIG. 4, a set of actuators 110 and 112 represent theactuators 34 and 56 depicted in FIGS. 2 and 3, respectively. A pluralityof sensors 114, 116, 118 and 120 are also shown and represent thevarious sensors disclosed and discussed above. Each of the VFDs 106 and108, the actuators 110 and 112, and the sensors 114, 116, 118 and 120are connected to a control unit 122 by way of electrical wiring 124 suchas a dedicated harness. Alternatively, the electrical wiring could be acommon bus such as in a controller area network. The control unit 122receives signals from the various sensors 114, 116, 118, and 120,processes the information it receives, and then sends out commandsignals to the VFDs 106 and 108 and the actuators 110 and 112. The VFDs106 and 108 then interpret the command signals and send correspondingdrive signals to the fans 102 and 104, respectively. In the abovedescribed embodiment, a drive signal includes a signal from a powersupply having an appropriately modulated frequency.

Through proper programming of either control unit 122, VFDs 106 and 108,or both, maximum speed settings may be established for the fans 102 and104. Likewise, minimum speed settings may be set. Furthermore, parameterset points may be established for the overall operation and logic of thesystem. For example, a temperature value at which the storage bin is tobe maintained may be defined. Having a defined temperature value andsensing air temperature at various points in the stream of air flow, thesystem will operate to adjust fan speed and/or adjust the mix of airflow to alter an existing environmental parameter. The logic ofcontrolling the environment with such a system will be discussed ingreater detail below.

It is noted that with such a system, greater flexibility is realizedthrough the use of variable-speed drives. By using VFDs or some othervariable-speed drive, more gradual changes to the environment may beachieved. The possibility of reduced power consumption is also seen inthe practice of the present technique. This is because the relationshipbetween power consumption and fan speed is nonlinear. For example, ithas been established that in a system similar to that described herein,a twenty percent reduction in fan speed results in a fifty percentreduction in power consumption. Knowing that the rate of air flow varieslinearly with fan speed, a simple calculation may be performed tocompare air flow and power consumption for a system operating at fullspeed with a system operating at a reduced fan speed of eighty percent.A system operating at full power may circulate air, for example, at100,000 cfm (cubic feet per minute). This system will circulate6,000,000 cubic feet of air in a given hour. The reduced-speed system,however, will circulate air at a rate of 80,000 cfm requiring an hourand fifteen minutes to circulate 6,000,000 cubic feet of air. However,even with the additional fifteen minutes of operating time, thereduced-speed system only consumes sixty-two and a half percent as muchpower as the full-speed system. Indeed, operating the fan at even slowerspeeds nets even larger savings in power.

With reduced-fan speed consuming considerably less energy than doesfull-speed operation, a fan can be operated continuously to maintain thestorage facility environment within a tightly defined parameter range.For example, if the storage facility is desired to be maintained at atemperature of 50° F., the fans can be operated continuously at areduced speed to maintain the temperature within a few degrees.Furthermore, with proper fan speed control, in conjunction with properinlet ventilation control, temperature can be maintained within a rangeof approximately 1° F. Thus, large temperature spikes may be eliminatedfrom the storage environment with reduced power consumption.

It is noted that while the schematic of FIG. 4 shows a single controlunit 122, it is possible that multiple controllers be employed inoperation of the system 100. For example, the overall system 100 couldbe subdivided into subsystems wherein the main fan 102 and drive 106were considered an individual subsystem. Similarly, the control of theauxiliary fan 104, drive 108 and auxiliary actuator may be takentogether as a subsystem. Indeed, a subsystem may simply include acontrolling actuator-associated main ventilation inlet.

Turning now to FIG. 5, and with reference to FIG. 4, the logic employedaccording to one aspect of the present technique is discussed. First, aparameter set point 142 is defined. The parameter set point is the valueat which the storage facility environment should be maintained. Forexample, it may be a value concerning temperature, humidity, CO₂ or someother environmental parameter. For sake of clarity, and not by way oflimitation, the use of temperature will be maintained as the specificenvironmental parameter throughout the following discussion.

Maximum and minimum fan speeds are defined, as shown at step 144, andare programmed into either the control unit 122 or the VFD 106(illustrated in FIG. 4). Alternatively, maximum and minimum powerconsumption rates may be defined for the fans. An environmentalparameter is then sensed 146 and an appropriate data signal iscommunicated to the control unit 122. The control unit 122 thendetermines if the sensed temperature is greater than the defined setpoint as indicated at 148. If the result is affirmative, then thecontrol unit 122 determines whether the current fan speed is less thanthe defined maximum as shown at step 150. If this inquiry isaffirmative, then the control unit 122 will increase the speed of thefan 102 as indicated at step 152. Following the increase of fan speed,the temperature is again sensed as shown at step 146, with the processready to repeat itself. If the inquiry at step 154 is answerednegatively, then the fan speed is maintained at the maximum speed andthe process returns to step 146.

If, however, the inquiry at 148 yields a negative response, the controlunit 122 then will inquire whether the sensed temperature is less thanthe defined set point as shown at 156. If the result is affirmative, asecond inquiry is made as to whether the fan speed is greater than theminimum setting as indicated at step 158. If the result to this inquiryis affirmative, then the fan speed is reduced as shown at 160, and theprocess returns to step 146. If the inquiry at step 158 yields anegative response, then the fan speed is maintained at the minimum speedas shown at 162, and the process returns to step 146. Finally, if theinquiry at step 156 yields a negative result, the process likewisereturns to step 146.

Thus, using the logic described above, the fan is operated continuouslyand, if the maximum setting is less than full power, it is operatedcontinuously at a reduced speed. In the example above, the presenttechnique allows for the continuous control of fan speed to maintain thestorage facility environment at a defined temperature. It is noted thatthe chosen parameter need not be temperature. It is also noted that theabove logic is in reference solely to fan speed and that the controlunit may contemporaneously control the ventilation inlet 26 (shown inFIGS. 1 and 2) to influence the environment as well. Additionally, it isnoted that, in certain circumstances, fan speed may be decreased if thesensed parameter is greater than the defined set point and increased ifthe sensed parameter is less than the defined set point. The fan speedmay also be increased or decreased in response to the deviation of thesensed parameter from the set point or the difference between two sensedparameters.

Turning now to FIG. 6 and referring to FIG. 4, the operational logicregarding the operation of the auxiliary system of FIG. 3 is described.First, parameter set points are defined as shown at step 172. Both aninternal set point and an external set point are defined. The internalset point is a parameter value at which the storage facility environmentshould be maintained. For example, it may be a value concerningtemperature, humidity, CO₂ or some other environmental parameter. Forsake of clarity, the following example will focus on the control of CO₂as the internal parameter to be maintained. The external set point is aparameter value which is used to override the system in specificinstances. For this discussion, the external set point is defined interms of temperature.

While not shown specifically in FIG. 6, maximum and minimum fan speedsmay be defined according to the description in reference to FIG. 5. Aninternal environmental parameter is then sensed as shown at step 174,and an appropriate data signal is communicated to the control unit 122.Again, for this discussion the sensed internal parameter will be the CO₂level in the storage facility. An external parameter is also sensed asshown at 176. For this discussion, the external parameter will be theambient temperature outside the storage facility. The control unit 122then determines if the sensed CO₂ is less than the defined set point asindicated at 178. If the result is affirmative, then the control unit122 will decrease the speed of the auxiliary fan 104 as indicated at180. Following the decrease in fan speed, the process returns to step174. If the inquiry at step 178 is answered negatively, then the controlunit 122 determines whether the sensed CO₂ level is greater than thedefined level as indicated at 182. If the result is negative, then thespeed is maintained as shown at 184, and the process returns to step176. If, however, the result is affirmative, the control unit 122further determines if the external temperature is less than the externalset point as seen at step 186. If the result to the inquiry at 186 isaffirmative, then the fan speed is increased as shown at step 188 andthe process returns to step 176. If the result to the inquiry at 186 isnegative, the control unit 122 determines whether the sensed externaltemperature is greater than the external set point as shown at step 190.Again, if the result to this inquiry is negative, then the fan speed ismaintained as shown at step 184, and the process returns to step 176.If, however, the result to the inquiry at step 190 is affirmative, thenthe fan speed is decreased as shown at step 192 and the process returnsto step 176.

Thus, the inquiries shown at steps 186 and 190 work as a check on theexternal environment. This allows an override function to be in placesuch that the admittance of external air by the auxiliary system doesnot interfere with the maintenance of one or more other environmentalvalues. For example, if the main fan 102 is being utilized to controltemperature and the auxiliary fan 104 is being utilized to control CO₂,the use of external air to sweep out CO₂ may impair the system's abilityto control temperature, depending on the temperature of the externalair. Thus, the main fan 102 is given priority in the example above, suchthat control of temperature overrides the control of CO₂. Of course themain and auxiliary systems could each control parameters different thanthose attributed in the above example with similar logic employed andsimilar results achieved.

It should be understood that while the logic discussed in connectionwith FIGS. 5 and 6 related to a particular system, the logic may beapplied to the other systems or subsystems disclosed herein. Forexample, the logic of FIG. 5 may be easily adapted for use with theauxiliary system if so desired. Similarly, the logic discussed inconnection with FIG. 6 may equally be applied to operation of the mainfan or possibly the control of the main ventilation inlet. It is notedthat, as disclosed previously herein, the auxiliary fan may operate asthe primary control of the internal environment if so desired.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims. For example, it is contemplated that while theembodiments and techniques described above have been shown to becombined into a single system, they may operate as individual systems oras subsystems. For example, what has been described as the auxiliarysystem, i.e., FIG. 3, need not be connected to the same control unit asthe systems described in FIGS. 1 and 2. As noted above, multiplecontrollers may be employed to operate the system in a similar manner.

It is further contemplated that a single control unit may interact withindividual components of the system on an independent basis. Forexample, FIG. 4 illustrates a system with a single control unit 122networked with multiple components. Such a control unit 122 may beconfigured to receive information or data from a first sensor 114 anduse that information to control the speed of the first fan 102. Thecontrol unit 122 may then receive a signal from a second sensor 116 foruse in controlling the second fan 104. However, the first fan 102 may beoperated at a speed independent of the speed of the second fan 104.Likewise, contemporaneous and independent control may be exerted overthe ventilation inlets.

Of course, additional components may be introduced into the system foradded control and benefit. Such components may include, by way ofexample, heating equipment, cooling equipment, humidifiers,dehumidifiers, actuated exhaust controls, or fogging equipment for theintroduction of desired chemicals into the environment.

1. A method of controlling an internal environment of a storagefacility, the method comprising: providing at least one fan for inducingair movement within the storage facility; continuously operating the atleast one fan at less than full speed; flowing air through the at leastone fan, through an air plenum and into the storage facility; sensing atleast one environmental parameter within the air plenum; and varyingspeed of the at least one fan.
 2. The method according to claim 1,wherein sensing the at least one environmental parameter within the airplenum includes sensing temperature.
 3. The method according to claim 1,wherein sensing the at least one environmental parameter within the airplenum includes sensing humidity.
 4. The method according to claim 1,further comprising sensing at least one environmental parameter withinthe storage facility and selecting a value at which the at least oneenvironmental parameter within the storage facility should bemaintained.
 5. The method according to claim 4, further comprisingvarying the speed of the at least one fan according to a relationshipbetween the least one environmental parameter within the air plenum andthe at least one environment parameter within the storage facility. 6.The method according to claim 1, further comprising admitting externalair into the internal environment and regulating flow of the externalair in response to the at least one sensed environmental parameterwithin the air plenum.
 7. The method according to claim 6, whereinregulating flow of the external air includes regulating the flow of theexternal air independent of the speed of the at least one fan.
 8. Themethod according to claim 1, further comprising sensing at least oneparameter of an environment external to the storage facility.
 9. Themethod according to claim 8, further comprising varying the speed of theat least one fan according to the at least one sensed parameter of theenvironment external to the storage facility.
 10. The method accordingto claim 8, wherein sensing the at least one parameter of the externalenvironment includes sensing ambient temperature.
 11. The methodaccording to claim 8, wherein sensing the at least one parameter of theexternal environment includes sensing humidity.
 12. The method accordingto claim 8, further comprising admitting external air into the internalenvironment and regulating flow of the external air in response to theat least one sensed parameter of the external environment.
 13. A methodof controlling an internal environment of a storage bin containing amass of produce, the method comprising: flowing air through at least onefan, through at least one air plenum, through at least a portion of themass of produce and into the storage bin so as to induce continuous airmovement within the storage bin; providing at least a second fan forinducing introduction of external air into the storage bin; flowing airthrough the at least a second fan and out of the storage bin; sensing atleast one environmental parameter within the storage bin; and varyingspeed of the at least a second fan.
 14. The method according to claim13, further comprising continuously operating the at least one fan atless than full speed.
 15. The method according to claim 14, whereinsensing the at least one environmental parameter within the storage binincludes sensing a parameter selected from the group consisting oftemperature, carbon dioxide, and humidity.
 16. The method according toclaim 14, further comprising selecting a value at which the at least oneenvironmental parameter within the storage bin should be maintained andvarying the speed of the at least a second fan according to arelationship between the at least one environmental parameter within thestorage bin and a value at which the at least one environmentalparameter within the storage bin should be maintained.
 17. The methodaccording to claim 14, further comprising inducing introduction ofexternal air into the storage bin and regulating flow of the externalair in response to the at least one sensed environmental parameterwithin the storage bin.
 18. The method according to claim 14, furthercomprising sensing at least one parameter of an environment external tothe storage bin and varying the speed of the at least a second fanaccording to the at least one sensed environmental parameter external tothe storage bin.
 19. The method according to claim 18, wherein sensingthe at least one parameter of the external environment includes sensingambient temperature.
 20. The method according to claim 18, whereinsensing the at least one parameter of the external environment includessensing humidity.
 21. The method according to claim 18, furthercomprising admitting external air into the internal environment andregulating flow of the external air in response to the at least onesensed parameter of the environment external to the storage facility.22. The method according to claim 14, further comprising selecting amaximum fan speed and a minimum fan speed wherein the maximum fan speedis a reduced fan speed, and continually operating the at least a secondfan at a speed between the selected maximum and minimum fan speeds. 23.The method according to claim 14, further comprising selecting a maximumpower level and a minimum power level for input to the at least one fanwherein the maximum power level is a reduced power level, andcontinually operating the at least a second fan at a speed between theselected maximum and minimum power levels.
 24. A system for controllingan internal environment of a storage facility having an air plenum, thesystem comprising: at least one fan adapted to induce air movementthrough the air plenum and within the storage facility throughcontinuous operation; at least a second fan adapted to induceintroduction of external air to the storage facility; a variable-speeddrive coupled to the at least a second fan, wherein the variable-speeddrive provides a drive signal to the at least a second fan forcontrolling speed of the at least a second fan; at least one sensoradapted to determine at least one internal environmental parameter; atleast one electrical control unit coupled to the at least one sensor andto the variable-speed drive, wherein the at least one electrical controlunit receives a parameter signal indicative of the at least one internalenvironmental parameter from the at least one sensor and provides acommand signal to the variable-speed drive based upon the parametersignal for varying an operational speed of the at least a second fan;and a ventilation inlet wherein air external to the storage facility isadmitted into the internal environment.
 25. The system of claim 24,wherein the at least one sensor includes at least a temperature sensor,a carbon dioxide sensor, or a humidity sensor.
 26. The system of claim24, further comprising at least one additional sensor adapted todetermine at least one parameter of an environment external to thestorage facility wherein the at least one additional sensor is coupledto the at least one electrical control unit and provides an externalparameter signal to the at least one electrical control unit.
 27. Thesystem of claim 24, wherein the variable-speed drive is adapted to havea maximum speed setting and a minimum speed setting such that the atleast a second fan is continuously running between the maximum andminimum speed settings.
 28. The system of claim 24, further comprisingat least another variable-speed drive coupled to the at least one fan,wherein the at least another variable-speed drive is configured tooperate the at least one fan continuously at a reduced speed.
 29. Amethod of controlling an internal environment of a storage bin, themethod comprising: providing at least one fan for inducing continuousair movement within the storage bin; providing at least a second fan forinducing introduction of external air into the storage bin; flowing airthrough the at least a second fan and out of the storage bin; sensing atleast one environmental parameter within the storage bin; and sensing atleast one parameter of an environment external to the storage bin andvarying the speed of the at least a second fan according to the at leastone sensed environmental parameter external to the storage bin.